Highly selective detection of Au3+ using rhodamine-based modified polyacrylic acid (PAA)-coated ITO

Rhodamine derivatives grafted on polyacrylic acid (PAA) were designed, synthesized and evaluated as a Au3+-selective chemosensor using the rhodamine ring-opening approach. The fluorogenic and chromogenic polymer chemosensors (PAA-Rho1-PAA-Rho4) were constructed via a coupling reaction between PAA and alkylene polyamine groups possessing a different number of donor atoms and chain lengths to yield PAA-Rho1 (84.2%), PAA-Rho2 (80.3%), PAA-Rho3 (91.9%), and PAA-Rho4 (85.1%). Chemical structures and purity of polymeric sensors were characterized by TGA, NMR, TEM and IR. The complexation studies indicate that PAA-Rho3 exhibited the highest selectivity and sensitivity responsive colorimetric and fluorescence Au3+-specific sensor when compared to other metal ions and polymeric sensors. The polymeric sensors are non-fluorescence in the spirolactam form and could be selectively converted into the fluorescence ring-opened amide form in the presence of Au3+, leading to the fluorescence enhancements and colorimetric changes. In addition, the fluorescent conjugated polymer film as the chemosensors were fabricated by chemical modification on ITO substrate, which created new fluorescent film sensors (PAA-Rho3-ITO). Further study showed that the sensing process is reversible by rinsing with EDTA solutions; the lower detection limit was less than that obtained from uncoated polymer film PAA-Rho3, and the response time was less than 40 s. The super sensitive response, good reversibility, and very fast response time, make the fluorescent film sensors a promising Au3+ sensor for environmental and biological applications.145